[Week 10] Clarify how MCTS works & cleanup notebook (#425)
[Week 10] Clarify how MCTS works & cleanup notebook (#425)

* [Week 10] Clarify how MCTS works & cleanup notebook

* [Week 10] Comment on usage of select_best_leaf() in expand()

* [Week 10] Clarify exploration parameter and add theory notes

[Week 10] Rephrase definitions and fix typos

[Week 10] Fix typo in formula parameter and rephrase mention about it

[Week 10] Rephrase a mention about the tree policy

* [Week 10] Rephrase mention the tree policy

Co-authored-by: ivan_kharitonov <5c490c036f50baf9d04c9ad0a6582d619415809f@gmail.com>
yandexdataschool/Practical_RL,yandexdataschool/Practical_RL